The Math of Equations

The Math of EquationsStoichiometrythe calculation of quantities in chemical reactionsLimiting ReactantCalculate the amount of product that could be made for each reactantCompare the amount that could be made to the amount of product actually made to determine which reactant is limitingCalculate the excess reactant by calculating the amount that actually reacts and then subtractingLimiting ReactantThere is always some unreacted chemicalBecause you cannot measure to the last atomSo one reactant gets used up firstOnce one reactant is used up, no more product can be madeThe Chemical used up first is theLIMITING REACTANT

So.. reactant that is not all used up in the reactionExcess reactant 1.Determine the limiting reactant when..4 grams of H2 are reacted with 31g of O2. Determine moles of products each reactant can formThe one that is limiting will form the least amount of product2H2 +O2 2H2O4g H2 x 1 mole H2 x 2 moles H2O = 2 moles H2O 2 g H2 2 moles H2

31g O2 x 1 mole O2 x 2 moles H2O = 1.93 moles H2O 32 g O2 1 moles O2

Oxygen would run out first, thats why it makes less water.Oxygen is the limiting reactant

Mg + 2HCl MgCl2 + H2 3.500 g of Mg is added to 300.0 mL of 1.000 M HCl How many grams of Magnesium chloride are formed?3.500g Mg x 1 mole x 1 mole MgCl2 x 95.21 g MgCl2 = 13.71g MgCl2 24.31 1 mole Mg mole MgCl2 0.3000L x 1.000mole x 1 mole MgCl2 x 95.21 g MgCl2 = 14.28gMgCl2 1 L 2 mole HCl mole MgCl2

Since Mg runs out first, it is the limiting reactant.What test could you run to determine there was acid left over?Mg + 2HCl MgCl2 + H23.5 g of Mg is added to 300.0 mL of 1.0M HCl How many liters of gas @ STP?Since magnesium is the limiting reactant3.500g Mg x 1 mole x 1 mole H2 x 22.4 L H2 = 6.450 L H2 24.31 1 mole Mg mole H2Mg + 2HCl MgCl2 + H2What is left over and how many moles?If magnesium is the LR, then HCl is left over

3.500g Mg x 1 mole x 2 mole HCl = .2879 moles HCl used in reaction 24.31 1 mole Mg 0.3000L x 1.000mole HCl = .3000 moles HCl given 1 L 0.3000 moles HCl - 0.2879 (moles HCl used by Mg) = .0121 mols HCl

0.0121moles HCl = .0403 M .0121moles HCl x 36.5g = 0.4417g 0.3000L mole HClInterpreting Balanced equations2H2O 2H2 + O2

2 molecules 2 molecules + 1 molecule

2 mole 2 mole + 1 mole

Steps in stoichiometryWrite symbols and balanceWrite the moles on top/known on bottomCircle the known and unknownDo Dimensional analysis problemMole Mole problemsAmmonium nitrate decomposes to yield dinitrogen monoxide and waterHow many moles of water are produced if 14.8 moles of ammonium nitrate react?Write symbols and balanceWrite the moles on top/known on bottomCircle the known and unknownDo Dimensional analysis problempracticeBubbles of hydrogen gas and iron(III) chloride are produced when iron is dropped into hydrochloric acidHow many moles of hydrogen are produced when 14.5 moles of iron react?

Mole Mass problemsAluminum and silver nitrate react. How many moles of aluminum nitrate will be produced if 34.6 g of aluminum react?Write symbols and balanceWrite the moles on top/known on bottomCircle the known and unknownDo dimensional analysis problemMass-MassLithium nitride reacts with water to produce ammonia and lithium hydroxide.How many g of LiOH are produced if .38g of Li3N react?

OtherSodium chloride is produced when chlorine reacts with sodium1.How many L of Chlorine are needed to make 45.6 g sodium chloride?2.How many F.U. of NaCl are produced when 1.32 x 1015 atoms of Na react?

Law of Conservation of MatterProve the law of conservation of matter for

2NH3 N2 + 3H2Do Dimensional analysis problem for each reactant and product to determine the mass in g% Yield (product)% Yield = Actual (experiment) x 100%(product)Theoretical (calculation)You Try

13.5 g of sodium metal reacts with excess hydrochloric acid. How many liters of hydrogen are produced (at STP 22.4L / mol)13.5g Na x 1 mol Na x 1 mol H2 x 22.4L H2 = 23.0 g Na 2 mol Na 1 mol H2 2Na + 2HCl 2 NaCl + H2Steps to solvePredict productsBalance equationSet up Dimensional analysisSolve6.57 liters of H2 gas 4Al + 3O2 2Al2O3

x 102.g Al2O3 = 1 mol Al2O31 mole 27.01 gx 2 mol Al2O3 4 mole Al28.3 g aluminum oxide15.0 g of aluminum are reacted with excess oxygen. How much oxide was produced?15.0g xMatter is Conserved 4g + 32g = 36gIf you react 8 grams of hydrogen and 64 g of oxygen,how much water would did you make?Four Moles of H2O!Or 4 x 18 g/mole = 72 grams2H2 + O2 > 2H2O

8g + 64g = ??g8g + 64g = 72gHow many grams of water are produced from 2 moles of hydrogen gas and 1 mole of oxygen gas?2 moles of H2 = how many grams?2 mole x 2 atoms x 1 g/mole = 4g1 mole of O2 = how many grams? 2 atom x 16 g/mole = 32 g2 mole of H2O =how many grams2 mole x 18 g/mole=36g2H2 + O2 > 2H2O

4g 32g 36g